Morphological measurement of the nasal and paranasal cavities were
performed by means of the magnetic resonance imaging (MRI) technique.
Three-dimensional acoustic tube models were constructed using the MRI data.
Using the finite element method (FEM), the Helmholtz equation was solved for
sinusoidal pressure wave input at the velopharyngeal port to obtain sound
pressure, particle velocity, and sound intensity in the nasal cavity. In the
FEM modeling, the nasal tract containing the paranasal sinuses is divided into
3470 meshes and 4625 nodes. The cross-sectional shape of the tract was
approximated by an elliptical shape whose area and circumference were matched
to the observed data. The frequency transfer function as a ratio of sound
pressure at the velopharyngeal port to that at the nostrils, and input
impedance at the velopharyngeal port were calculated and compared with those of
the classical electric circuit model of the nasal tract. A FEM model
incorporating shape asymmetry between the left and right passages as defined by
the MRI observation was compared with that of the hypothetical models having
symmetrical shapes. The results showed that the complicated spectral shape of
nasal sounds can be successfully accounted for using the 3-D FEM approach.